As a thin film transistor (TFT) is a kind of key control unit for a display, the performances of the TFT are particularly important. In preparation processes of amorphous silicon thin-film transistors (a-Si TFTs), molybdenum (Mo) metal or molybdenum/aluminum-neodymium (Mo/AlNd) alloy is generally used for preparing a gate electrode. However, as the resistance of Mo metal or Mo/AlNd alloy is relatively high, in the process of manufacturing a large-size display, the current in a central portion of a display area may be less than that in a peripheral portion, and hence the problem of nonuniform displayed image may occur.
In order to solve the above problem, a low-resistance material (such as copper or aluminum) is mostly employed for a gate electrode and applied to the process of manufacturing a large-size display. However, as the low-resistance material has low adhesion with a substrate and a semiconductor, the problem of poor contact with an electrode material tends to occur. Moreover, the low-resistance material can react with silicon at a relatively low temperature and then be diffused to an active layer, and hence the performances of a device can be disadvantageously affected. The low-resistance material, e.g., copper, the electric resistivity of which is only 2 μΩ·cm, presents significant superiority as an electrode material.
Therefore, an anti-diffusion layer must be prepared on the low-resistance material. Currently, a metal with high melting point and an oxide or nitride thereof are commonly used for the anti-diffusion layer. In the application, tantalum dioxide (TaO2) with good anti-diffusion performance is usually selected to prepare an anti-diffusion layer. The preparation method usually adopts physical vapor deposition (PVD) or chemical vapor deposition (CVD).